Mutations in the glucokinase regulatory protein gene in 2p23 in obese French caucasians

Abstract

Aims/Hypothesis. Glucokinase regulatory protein (GKRP) controls the activity of glucokinase in liver but possibly also in some areas of the central nervous system, suggesting that it could play a role in body mass control. Its gene is located in a region (2p21-23) linked to serum leptin levels. Our goal was to investigate whether mutations in the GKRP gene were associated with obesity. Methods. Mutations were sought in the GKRP gene of 57 patients from the families of the French genomewide scan for obesity that contributed most to the positive LOD score with 2p21-23. The identified mutations were further sought in 720 unrelated obese individuals and 384 individuals of normal weight and their effect on the properties of recombinant GKRP were investigated. Results. The most frequent mutation (Pro446Leu) had a similar allele frequency in the obese (0.63) and normal weight (0.64) subjects and did not affect the properties of GKRP. Similarly, no effect on the properties of GKRP was observed with Arg590Tyr, found in 10 out of 720 obese subjects and in 2 out of 384 control subjects (p=0.18). Mutation Arg227Stop was found in one obese family and in 1 out of 384 control subjects and led to an insoluble protein. Mutation Arg518Gln, replacing a conserved residue, led to a marked decrease in the affinity of GKRP for both fructose 6-phosphate and fructose 1-phosphate and to a destabilization of GKRP. However, this mutation did not co-segregate with obesity in the single family in which it was found. Conclusions/interpretation. Mutations that affect the properties of GKRP are found in the French population, but they do not seem to account for the linkage between the 2p23 locus and quantitative markers of obesity. [Diabetologia (2003) 46:704-711]

The Common P446L Polymorphism in GCKR Inversely Modulates Fasting Glucose and Triglyceride Levels and Reduces Type 2 Diabetes Risk in the DESIR Prospective General French Population

“…It is tempting to propose that the P446L variant replacing a residue conserved between mammals might be the causative variant. However, one previous study having investigated the sensitivity of the GCKR-L446 mutant to fructose 6-and 1-phosphate, using rat GCKR, did not report any effect compared with the wild-type protein (7). Differential regulatory features between human and rat GCKR (18) could have masked a functional consequence of the L446 variant, or a more subtle, distinct defect acting on either GCK or another target protein remains to be discovered.…”

“…The HapMap II CEU data (www.hapmap.org) showed that rs780094 is in strong linkage disequilibrium (r 2 ϭ 0.932) with a non-synonymous GCKR variant (Pro446Leu, rs1260326) that we previously identified by the DNA sequencing of French individuals (7). Marju Orho-Melander and colleagues recently communicated their fine-mapping data showing the strongest signal for TG levels at the coding single nucleotide polymorphism (SNP) (rs1260326; P ϭ 1.5 ϫ 10 Ϫ9 ), with lesser associations to fasting glycemia and insulin sensitivity (M. Orho-Melander, O. Melander, V. Lyssenko, for the DGI, unpublished data).…”

“…Heterozygous mutations in GCK resulting in a reduction of enzymatic activity are responsible for a subtype of monogenic diabetes (maturity-onset diabetes of the young-2) (1,6). Previous genetic studies at the GCKR locus have not reported intragenic mutations associated with type 2 diabetes in humans (7,8).…”

Common Missense Variant in the Glucokinase Regulatory Protein Gene Is Associated With Increased Plasma Triglyceride and C-Reactive Protein but Lower Fasting Glucose Concentrations

“…The Pro446Leu variant has been introduced into rat cDNA but was not found to affect the functional properties of the rat protein when prepared by overexpression in Escherichia coli (34). Unfortunately, the human protein could not be produced using that expression system (32).…”

Correlation of rare coding variants in the gene encoding human glucokinase regulatory protein with phenotypic, cellular, and kinetic outcomes

“…We were able to determine the likely phase for 24 of 28 of the compound heterozygotes through family studies and/or inference from other individuals harboring the same rare allele (Supplemental Table 2 While preliminary comparisons of the collective group of individuals with rare variants with the WT reference group suggested a relationship to triglycerides, we were concerned that the merging of data from certain nonsynonymous variants of potentially no consequence with that of those that cause significant loss or gain of function could considerably diminish the power of the analysis. Finding large numbers of individuals with specific GCKR variants for detailed phenotyping was impractical, given the rarity of these particular variants in 1000 Genomes (47) and previously published studies (11,48). It thus became imperative to explore evolutionary, cell biological, and biochemical characterization of each variant to evaluate their potential contribution to phenotypes.…”